Storage device

1. A storage device comprising: a first memory cell; a second memory cell; and a controller configured to: in response to receiving a first command set when the first memory cell is in a ready state, execute an erase operation on the first memory cell, the erase operation including a plurality of voltage application steps, and the first command set including an erase command and a first address of the first memory cell; and in response to receiving a second command set when the first memory cell is in the ready state, execute a divided erase operation on the first memory cell, the divided erase operation including a part, but not all, of the voltage application steps, said part being at least a part of one of the voltage application steps, and the second command set including a first command, the erase command, and the first address, wherein the first command set does not include the first command, and wherein an erase voltage level that is applied in a first step of the plurality of voltage application steps in the erase operation is the same as an erase voltage level that is applied in a first or only step of said at least the part of the voltage application steps in the divided erase operation.

2. The storage device of claim 1 , wherein the first command is a command other than a read command, a write command, and the erase command.

3. The storage device of claim 1 , wherein the controller is configured to, in response to receiving a third command set after the second command set, execute a read or write operation on the second memory cell and subsequently execute another divided erase operation on the first memory cell, the another divided erase operation including another part of the voltage application steps, and the third command set including a second command, a read or write command, and a second address of the second memory cell.

4. The storage device of claim 3 , wherein the controller is configured to: in response to receiving a fourth command set after the second command set, execute the read or write operation on the second memory cell, the fourth command set including the read or write command and the second address; and in response to receiving a fifth command set after the fourth command set, execute the another divided erase operation on the first memory cell, the fifth command set including a third command, the erase command, and the first address.

5. The storage device of claim 1 , further comprising a register configured to store suspend information when the erase operation or the divided erase operation is suspended during a given one of the voltage application steps, the suspend information including a time period between a timing when the given one of the voltage application steps is started and a timing when the erase operation or the divided erase operation is suspended, wherein the controller is configured to resume the erase operation or the divided erase operation based on the suspend information.

6. The storage device of claim 1 , further comprising a storage unit configured to store a table in which first information is registered, the first information correlating at least one of end timings of the voltage application steps to an end timing of the divided erase operation.

7. A controlling method of a storage device, the method comprising: receiving a first command set when a first memory cell is in a ready state, and executing, in response to the first comment set, an erase operation on the first memory cell, the erase operation including a plurality of voltage application steps, and the first command set including an erase command and a first address of the first memory cell; and receiving a second command set when the first memory cell is in the ready state at a different time from when the first command set is received, and executing, in response to the second command set, a divided erase operation on the first memory cell, the divided erase operation including a part, but not all, of the voltage application steps, said part being at least a part of one of the voltage application steps, and the second command set including a first command, the erase command, and the first address, wherein the first command set does not include the first command, and wherein an erase voltage level that is applied in a first step of the plurality of voltage application steps in the erase operation is the same as an erase voltage level that is applied in a first or only step of said at least the part of the voltage application steps in the divided erase operation.

8. The method of claim 7 , wherein the first command is a command other than a read command, a write command, and the erase command.

9. The method of claim 7 , further comprising receiving a third command set after the second command set, and executing, in response to the third command set, a read or write operation on a second memory cell and subsequently executing another divided erase operation on the first memory cell, the another divided erase operation including another part of the voltage application steps, and the third command set including a second command, a read or write command, and a second address of the second memory cell.

10. The method of claim 7 , further comprising: receiving a fourth command set after the second command set, and, in response to the fourth command set, executing a read or write operation on the second memory cell, the fourth command set including a read or write command and a second address of the second memory cell; and receiving a fifth command set after the fourth command set, and executing, in response to the fifth command set, another divided erase operation on the first memory cell, the another divided erase operation including another part of the voltage application steps, and the fifth command set including a third command, the erase command, and the first address.

11. The method of claim 7 , further comprising storing suspend information when the erase operation or the divided erase operation is suspended during a given one of the voltage application steps, the suspend information including a time period between a timing when the given one of the voltage application steps is started and a timing when the erase operation or the divided erase operation is suspended, and resuming the erase operation or the divided erase operation based on the suspend information.

12. The method of claim 7 , further comprising storing a table in which first information is registered, the first information correlating at least one of end timings of the voltage application steps to an end timing of the divided erase operation.

13. The storage device of claim 1 , wherein the controller is configured to: in response to receiving a fifth command set when the first memory cell is in a busy state after the second command set is received, suspend the divided erase operation after elapse of a first period from when the fifth command set is received, and execute a read or write operation on the second memory cell, the fifth command set including a fourth command, a read or write command, and a second address of the second memory cell; and in response to receiving a sixth command set when the first memory cell is in a busy state after the second command set is received, suspend the divided erase operation after elapse of a second period from when the sixth command set is received, and execute the read or write operation on the second memory cell, the sixth command set including a fifth command, the read or write command, and the second address, wherein the first period is shorter than the second period.

14. The storage device of claim 13 , wherein the controller is configured to: in response to receiving a seventh command set after the fifth command set, resume the divided erase operation with application of a first erase voltage, the seventh command set including a sixth command, the erase command, and the first address; and in response to receiving the seventh command set after the sixth command set, start another divided erase operation with application of a second erase voltage, the another divided erase operation including another part of the voltage application steps, and the second erase voltage being higher than the first erase voltage.

15. The storage device of claim 1 , wherein the controller is configured to: in response to receiving an eighth command set after the second command set, execute another divided erase operation on the first memory cell, the another divided erase operation including another part of the voltage application steps, and the eighth command set including a seventh command, the erase command, and the first address; and in response to receiving the eighth command set again, execute still another divided erase operation on the first memory cell, the still another divided erase operation including still another part of the voltage application steps.

16. The method of claim 7 , further comprising: receiving a fifth command set when the first memory cell is in a busy state after the second command set is received, and suspending, in response to the fifth command set, the divided erase operation after elapse of a first period from when the fifth command set is received, and executing a read or write operation on the second memory cell, the fifth command set including a fourth command, a read or write command, and a second address of the second memory cell; and receiving a sixth command set when the first memory cell is in a busy state after the first command set is received, and suspending, in response to the sixth command set, the divided erase operation after elapse of a second period from when the sixth command set is received, and executing the read or write operation on the second memory cell, the sixth command set including a fifth command, the read or write command, and the second address, wherein the first period is shorter than the second period.

17. The method of claim 16 , further comprising: receiving a seventh command set after the fifth command set, and resuming, in response to the seventh command set, the divided erase operation with application of a first erase voltage, the seventh command set including a sixth command, the erase command, and the first address; and receiving the seventh command set after the sixth command set at a different time from when the first command set is received, and starting, in response to the seventh command set, another divided erase operation with application of a second erase voltage, the another divided erase operation including another part of the voltage application steps, and the second erase voltage being higher than the first erase voltage.

18. The method of claim 7 , further comprising: receiving an eighth command set after the second command set, and executing, in response to the eighth command set, another divided erase operation on the first memory cell, the another divided erase operation including another part of the voltage application steps, and the eighth command set including a seventh command, the erase command, and the first address; and receiving the eighth command set again, and executing, in response to the eighth command set, still another divided erase operation on the first memory cell, the still another divided erase operation including still another part of the voltage application steps.

19. The storage device of claim 5 , wherein: the voltage application steps include a first application with a first level of an erase voltage and a second application with a second level of the erase voltage, the first application being followed by the second application, and the second level being higher than the first level, the timing when the erase operation or the divided erase operation is suspended is in a timing during the first application, and the suspend information includes a time period between a timing when the first application is started and the timing when the erase operation or the divided erase operation is suspended.

20. The storage device of claim 5 , wherein the erase operation further includes a plurality of verify operations, and wherein each of the voltage application steps includes at least one voltage apply operation and is followed by one of the plurality of verify operations.

21. The storage device according to claim 5 , wherein the controller is configured to suspend the erase operation at an intermediate point of the given one of the voltage application steps in response to receiving a suspend command, and the controller is configured to resume the erase operation based on the suspend information such that the controller resumes the erase operation based on the timing when the erase operation or the divided erase operation was suspended.

22. The storage device of claim 1 , wherein the ready state is a state before stored data is erased.